656 



MR. C. A. MATLEY ON THE 



[Aug. 1899, 



(e) Disruption. 



Instances of the partial breaking-up of bands of rock may be noted 

 outside the bounds of the crush-conglomerates thenaselves. An 

 excellent example is to be seen in the Ordovician of Forth Newydd, 

 a cove situated north-west of Mynachdy, near the western end of 

 the Northern District boundary-fault. The ordinary black Ordo- 

 vician shales are here interstratified with courses of grit, and the 

 breaking-up of these grit-bands is shown in the cliff in the clearest 

 manner. The appended sketch (fig. 7) shows that these courses are 



Pig. 7. — Disrupted grit-courses in Ordovician blacJc shales, 

 Po7^th Neiuydd. 



[The two lowest grit-bands are introduced from another part of the section.] 



broken into longer or shorter pieces, lying quite dissociated one from 

 the other, and strong transverse cracks indicate the commencement 

 of further disruption. The ends of some of the pieces are pointed, 

 those of others bluntly rounded. One of the bands has become a string 

 of phacoids or lenticles, which a very little more pinching would have 

 separated into distinct pieces. The shales have a general undu- 

 lating dip to the north, and would not of themselves have suggested 

 that the strata had been subjected to such powerful forces as those 

 to which the disrupted grits testify. A little farther south more 



